Damaged body panels in automobiles and other motor vehicles typically are repaired by bending or hammering the metal to a shape which approximates the original contour of the body panel. A layer of body putty then is applied to the repaired surface of the panel, causing the putty to fill wrinkles and other minor imperfections in the exterior surface of the panel. After the body putty sets to a desired degree of hardness, the surface of the panel is restored to the original surface contour by removing body putty in excess of the surface contour. This putty removal, or at least the final finishing steps of removal, takes place by sanding the surface of the panel to remove high spots of putty and to provide a smooth overall surface finish. This sanded finish must blend with the metal on adjacent undamaged portions of the panel, and also must duplicate the original shape or contour of the panel, in order to provide a professional repaired surface that, after being painted, is visually indistinguishable from the original undamaged surface.
Body panels having only flat surfaces or rounded contours of relatively large radius, but lacking relatively sharp contours or curvilinear features, can be finished using power disk sanders or the like, as the repaired and original portions of the flat or large-radius curved surfaces are more readily blended together. However, relatively linear or elongated surface contours (as found, for example, on door panels) generally must be sanded by hand to blend the sanded finish with the original contour of the panel. This manual sanding usually requires a back-and-forth sanding movement paralleling the linear contour, and for the best result the manual sander or other repair tool should move in parallel alignment with the longitudinal extent of the body contour. Body shop workers in the past either have done without a straightedge, or have improvised one using a yardstick or a similar wooden strip at hand, placing the straightedge against the body panel and visually comparing the straightness of the sanded area with the reference provided by the straightedge. This expedient is time-consuming and inexact, many body repairs take place without using a straightedge, relying on visual observation alone to maintain linear movement of the sander.
In addition to the problem of guiding a sander during a manual sanding operation, known manual sanding devices for sanding longitudinal contoured surfaces also are less than satisfactory. Contour sanders are known which seek to provide accurate contour sanding by matching the existing contour of an undamaged surface. One example of a prior-art contour sander is shown in U.S. Pat. No. 1,570,177. Such contour sanders have a number of individual blades arrayed in parallel within a holder. By pressing the blades against the desired contour while the holder is loosened, the edges of the blades will assume a complementary contour for attaching a piece of sandpaper or other abrasive material. However, such contour sanders of the prior art do not easily duplicate or reproduce a given contour having abrupt angles or other well-defined features.